There are a few fish by the rocks on the left side ( facing the water ) at Mullet, and also at the south end of Grand Case - though that area is tricky to enter and leave because of the rocks. As KC2SXM says, Creole Rock has a large number of fish, and you can book tours on a smalll ( 6 people ) boat operating out of Grand Case Beach Club. If you are used to snorkeling with lots of colorful fish, like St. Johns or St. Thomas, you may be a bit dissapointed. We do bring masks and one set of travel swim fins.